Aluminum alloy material and hydrogen embrittlement inhibitor for aluminum alloy materials

ABSTRACT

An aluminum alloy material having an aluminum alloy composition of the aluminum alloy compositions (1) below. 
     Aluminum alloy composition (1) 
     0.30 mass% or less of Si, more than 0.35 mass% of Fe, 0.20 mass% or less of Cu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% of Mg, 0.30 mass% or less of Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or less of V, 0.25 mass% or less of Zr, and 0.20 mass% or less of Ti, while additionally containing Al.

TECHNICAL FIELD

The present invention relates to an aluminum alloy material and to ahydrogen embrittlement inhibitor for aluminum alloy materials.

BACKGROUND ART

Aluminum alloy materials, which have a wide range of applications,suffer from the problem of hydrogen embrittlement cracks, and proposalshave been made to solve this problem (see PTL 1 to 4).

PTL 1 discloses an aluminum alloy material for a high pressure gasvessel, which has an aluminum alloy composition that contains, in termsof mass%, 4.0 to 6.7% of Zn, 0.75 to 2.9% of Mg, 0.001 to 2.6% of Cu,0.05 to 0.40% of Si, 0.005 to 0.20% of Ti and 0.01 to 0.5% of Fe, andcontains one or two or more of 0.01 to 0.7% of Mn, 0.02 to 0.3% of Cr,0.01 to 0.25% of Zr and 0.01 to 0.10% of V so as to satisfy therelationship 1.0% ≥ Fe+Mn+Cr+Zr+V ≥ 0.1%, with the remainder comprisingAl and unavoidable impurities, and in which the relationship betweenelectrical conductivity (%IACS) and the total content of Fe, Mn, Cr, Zrand V satisfies the following relationship: electrical conductivity (%)≥ -4.9×(Fe+Mn+Cr+Zr+V)+40.0, and which has a 0.2% proof stress of 275MPa or more and exhibits excellent hydrogen embrittlement resistance.

PTL 2 discloses a method for producing a thick aluminum alloy thickplate having excellent strength and ductility, in which a thick plate inwhich the total area ratio of intermetallic compounds having anequivalent circle diameter of more than 5 µm is controlled to 2% or lessis obtained by using an Al-Zn-Mg-Cu-based aluminum alloy, which contains5.0 to 7.0% of Zn, 1.0 to 3.0% of Mg and 1.0 to 3.0% of Cu, alsocontains a total of 0.05 to 0.5% of one or two or more of 0.05 to 0.3%of Cr, 0.05 to 0.25% of Zr, 0.05 to 0.40% of Mn and 0.05 to 0.35% of Sc,and further contains 0.25% or less of Si and 0.25% or less of Fe asimpurities, with the remainder comprising Al and unavoidable impurities,subjecting an ingot of this alloy to a homogenizing treatment by holdingthe ingot at a temperature of 450 to 520° C. for 1 hour or longer, thenregulating the average cooling rate at least to 400° C. to 100° C./hr ormore in a step for cooling the ingot, then carrying out hot rolling to aplate thickness of 50 mm or more at a temperature within the range 300to 440° C., and then carrying out a solution treatment, quenching and anartificial aging treatment.

PTL 3 discloses a method for producing a high strength Al-Zn-Mg-basedaluminum alloy forging material having excellent resistance to stresscorrosion cracking by regulating the Fe content in the alloy to 0.15 wt%or less when an aluminum alloy, which contains 4.5 to 8.5 wt% of Zn, 1.5to 3.5 wt% of Mg and 0.8 to 2.6 wt% of Cu and further contains at leastone of Mn, Cr, Zr, V and Ti, with the remainder comprising Al andimpurities, is molded into a forging material having an H-section byforging.

PTL 4 discloses a high strength aluminum alloy for welded structures,which exhibits excellent stress corrosion cracking resistance and whichcontains 5 to 8 wt% of Zn, 1.2 to 4.0 wt% of Mg, more than 1.5 wt% andnot more than 4.0 wt% of Cu, 0.03 to 1.0 wt% of Ag, 0.01 to 1.0 wt% ofFe, 0.005 to 0.2 wt% of Ti and 0.01 to 0.2 wt% of V, and furthercontains one or two or more of 0.01 to 1.5 wt% of Mn, 0.01 to 0.6 wt% ofCr, 0.01 to 0.25 wt% of Zr, 0.0001 to 0.08 wt% of B and 0.03 to 0.5 wt%of Mo, with the remainder comprising aluminum and unavoidableimpurities.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Application Publication No. 2009-221566-   PTL 2: Japanese Patent Application Publication No. 2011-058047-   PTL 3: Japanese Examined Patent Publication No. H01-025386-   PTL 4: Japanese Patent No. 2915487

SUMMARY OF INVENTION Technical Problem

However, no aluminum alloy materials are known that can effectivelyprevent or inhibit hydrogen embrittlement to the extent required in theaerospace industry.

The problem to be solved by the present invention is to provide: analuminum alloy material that can effectively prevent or inhibit hydrogenembrittlement; and a hydrogen embrittlement inhibitor for aluminum alloymaterials.

Solution to Problem

According to the present invention, it was found that hydrogenembrittlement could be prevented or inhibited by an aluminum alloymaterial having a specific alloy composition and by a hydrogenembrittlement inhibitor for aluminum alloy materials which comprisesspecific second phase particles, and the problem mentioned above wasthereby solved.

This type of alloy is novel. In PTL 1 to 4, the amount of Fe is higherthan that specified in Alloy No. 7050 in JIS H 4100: 2014 “Aluminum andAluminum Alloy Plates and Strips”, but all of these fall outside therange of the aluminum alloy material of the present invention.

For example, the composition of invention example 6 in table 1 in PTL 1contains 0.21 mass% of Si, 0.28 mass% of Fe, and the like, thecomposition of alloy A in table 1 on page 11 of PTL 2 contains 0.21mass% of Si, 0.28 mass% of Fe, and the like, the composition of sample 4in table 1 on page 4 of PTL 3 contains 0.10 mass% of Si, 0.19 mass% ofFe, and the like, and the composition of comparative alloy 10 in table 1on page 4 of PTL 4 contains 0.10 mass% of Si, 0.20 mass% of Fe, and thelike, but these compositions all fall outside the scope of the aluminumalloy material of the present invention.

The constitution of the present invention, which is a specific means forsolving the problem mentioned above, and a preferred constitution of thepresent invention will now be described.

[1] An aluminum alloy material which has an aluminum alloy compositionof any one of aluminum alloy compositions (1) to (7) below.

Aluminum Alloy Composition (1)

0.30 mass% or less of Si, more than 0.35 mass% of Fe, 0.20 mass% or lessof Cu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% of Mg, 0.30 mass% orless of Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or less of V, 0.25 mass%or less of Zr, and 0.20 mass% or less of Ti, while additionallycontaining Al.

Aluminum Alloy Composition (2)

0.12 mass% or less of Si, more than 0.15 mass% of Fe, 1.5 to 2.0 mass%of Cu, 0.10 mass% or less of Mn, 2.1 to 2.6 mass% of Mg, 0.05 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.05 mass% or less of Ni, 0.10 to0.16 mass% of Zr, and 0.06 mass% or less of Ti, while additionallycontaining Al.

Aluminum Alloy Composition (3)

0.12 mass% or less of Si, more than 0.25 mass% of Fe, 2.0 to 2.6 mass%of Cu, 0.10 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.06mass% or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (4)

0.40 mass% or less of Si, more than 0.50 mass% of Fe, 1.2 to 2.0 mass%of Cu, 0.30 mass% or less of Mn, 2.1 to 2.9 mass% of Mg, 0.18 to 0.26mass% of Cr, 5.1 to 6.1 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

Aluminum Alloy Composition (5)

More than 0.7 mass% of Si+Fe, 0.10 mass% or less of Cu, 0.10 mass% orless of Mn, 0.10 mass% or less of Mg, and 0.8 to 1.3 mass% of Zn, whileadditionally containing Al.

Aluminum Alloy Composition (6)

0.12 mass% or less of Si, more than 0.12 mass% of Fe, 2.0 to 2.6 mass%of Cu, 0.06 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.05mass% or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (7)

0.40 mass% or less of Si, more than 0.50 mass% of Fe, 1.6 to 2.4 mass%of Cu, 0.30 mass% or less of Mn, 2.4 to 3.1 mass% of Mg, 0.18 to 0.28mass% of Cr, 6.3 to 7.3 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

The aluminum alloy material set forth in [1] in which the aluminum alloycomposition is aluminum alloy composition (3).

The aluminum alloy material set forth in [1] or [2], which includessecond phase particles having a higher hydrogen trapping energy thanthat of a semi-coherent precipitate interface.

The aluminum alloy material set forth in [3], wherein the second phaseparticles are Al₇Cu₂Fe particles.

A hydrogen embrittlement inhibitor for aluminum alloy materials, whichcomprises Al₇Cu₂Fe particles and can prevent hydrogen embrittlement ofaluminum alloy materials.

The hydrogen embrittlement inhibitor set forth in [5], which can preventhydrogen embrittlement of an aluminum alloy material having aluminumalloy composition (A) below.

Aluminum Alloy Composition (A)

0.40 mass% or less of Si, 2.6 mass% or less of Cu, 0.70 mass% or less ofMn, 3.1 mass% or less of Mg, 0.30 mass% or less of Cr, 7.3 mass% or lessof Zn, and 0.20 mass% or less of Ti, while additionally containing Feand Al.

The hydrogen embrittlement inhibitor set forth in [5] or [6], which canprevent hydrogen embrittlement of an aluminum alloy material having anyone of aluminum alloy compositions (1) to (7) below.

Aluminum Alloy Composition (1)

0.30 mass% or less of Si, more than 0.35 mass% of Fe, 0.20 mass% or lessof Cu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% of Mg, 0.30 mass% orless of Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or less of V, 0.25 mass%or less of Zr, and 0.20 mass% or less of Ti, while additionallycontaining Al.

Aluminum Alloy Composition (2)

0.12 mass% or less of Si, more than 0.15 mass% of Fe, 1.5 to 2.0 mass%of Cu, 0.10 mass% or less of Mn, 2.1 to 2.6 mass% of Mg, 0.05 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.05 mass% or less of Ni, 0.10 to0.16 mass% of Zr, and 0.06 mass% or less of Ti, while additionallycontaining Al.

Aluminum Alloy Composition (3)

0.12 mass% or less of Si, more than 0.25 mass% of Fe, 2.0 to 2.6 mass%of Cu, 0.10 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.06mass% or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (4)

0.40 mass% or less of Si, more than 0.50 mass% of Fe, 1.2 to 2.0 mass%of Cu, 0.30 mass% or less of Mn, 2.1 to 2.9 mass% of Mg, 0.18 to 0.26mass% of Cr, 5.1 to 6.1 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

Aluminum Alloy Composition (5)

More than 0.7 mass% of Si+Fe, 0.10 mass% or less of Cu, 0.10 mass% orless of Mn, 0.10 mass% or less of Mg, and 0.8 to 1.3 mass% of Zn, whileadditionally containing Al.

Aluminum Alloy Composition (6)

0.12 mass% or less of Si, more than 0.12 mass% of Fe, 2.0 to 2.6 mass%of Cu, 0.06 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.05mass% or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (7)

0.40 mass% or less of Si, more than 0.50 mass% of Fe, 1.6 to 2.4 mass%of Cu, 0.30 mass% or less of Mn, 2.4 to 3.1 mass% of Mg, 0.18 to 0.28mass% of Cr, 6.3 to 7.3 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

The hydrogen embrittlement inhibitor set forth in [5] or [6], which canprevent hydrogen embrittlement of an aluminum alloy material having anyone of aluminum alloy compositions (A1) to (A7) below.

Aluminum Alloy Composition (A1)

0.30 mass% or less of Si, 0.35 mass% or less of Fe, 0.20 mass% or lessof Cu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% of Mg, 0.30 mass% orless of Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or less of V, 0.25 mass%or less of Zr, and 0.20 mass% or less of Ti, while additionallycontaining Al.

Aluminum Alloy Composition (A2)

0.12 mass% or less of Si, 0.15 mass% or less of Fe, 1.5 to 2.0 mass% ofCu, 0.10 mass% or less of Mn, 2.1 to 2.6 mass% of Mg, 0.05 mass% or lessof Cr, 5.7 to 6.7 mass% of Zn, 0.05 mass% or less of Ni, 0.10 to 0.16mass% of Zr, and 0.06 mass% or less of Ti, while additionally containingAl.

Aluminum Alloy Composition (A3)

0.12 mass% or less of Si, 0.15 mass% or less of Fe, 2.0 to 2.6 mass% ofCu, 0.10 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% or lessof Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.06 mass%or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (A4)

0.40 mass% or less of Si, 0.50 mass% or less of Fe, 1.2 to 2.0 mass% ofCu, 0.30 mass% or less of Mn, 2.1 to 2.9 mass% of Mg, 0.18 to 0.26 mass%of Cr, 5.1 to 6.1 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al. Aluminum alloy composition (A5)

0.7 mass% or less of Si+Fe, 0.10 mass% or less of Cu, 0.10 mass% or lessof Mn, 0.10 mass% or less of Mg, and 0.8 to 1.3 mass% of Zn, whileadditionally containing Al.

Aluminum Alloy Composition (A6)

0.12 mass% or less of Si, 0.12 mass% or less of Fe, 2.0 to 2.6 mass% ofCu, 0.06 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% or lessof Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.05 mass%or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (A7)

0.40 mass% or less of Si, 0.50 mass% or less of Fe, 1.6 to 2.4 mass% ofCu, 0.30 mass% or less of Mn, 2.4 to 3.1 mass% of Mg, 0.18 to 0.28 mass%of Cr, 6.3 to 7.3 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

Advantageous Effects of Invention

The present invention is capable of providing: an aluminum alloymaterial that can effectively prevent or inhibit hydrogen embrittlement;and a hydrogen embrittlement inhibitor for aluminum alloy materials.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a virtual cross section of a tomographic image of amicrostructure of a (High Fe) aluminum alloy material of Working Example1.

FIG. 2 is a virtual cross section of a tomographic image of a fracturesurface of the (High Fe) aluminum alloy material of Working Example 1.

FIG. 3 is a virtual cross section of a tomographic image of a (Low Fe)aluminum alloy material of Reference Example 2.

FIG. 4 is a virtual cross section of a tomographic image of a fracturesurface of the (Low Fe) aluminum alloy material of Reference Example 2.

FIG. 5 is a schematic diagram of separation at η/Al interfaces as aresult of hydrogen trapping.

FIG. 6 is a number line diagram of hydrogen trapping energies ofmicrostructures in an aluminum alloy material.

FIG. 7 is a schematic diagram of the crystal structure (space groupP4/mnc) of Al₇Cu₂Fe particles.

FIG. 8 is a bar chart showing trapped hydrogen amounts at sites in thealuminum alloy materials of Working Example 1 (High Fe) and ReferenceExample 2 (Low Fe).

FIG. 9 is a graph that shows the relationship between hydrogendistribution to IMC (Al₇Cu₂Fe) particles (H at IMC), hydrogendistribution to a semi-coherent precipitate interface (H at η₂), andhydrogen embrittlement (quasi-cleavage creak) area fraction QCF.

DESCRIPTION OF EMBODIMENTS

The present invention will now be explained in detail. Explanations ofthe constituent features described below are based on representativeembodiments and specific examples, but it should be understood that thepresent invention is not limited to such embodiments. Moreover,numerical ranges expressed using the symbol “-” mean ranges that includethe numerical values before and after the “-” as lower and upper limitsof the range.

Aluminum Alloy Material

In the aluminum alloy material of the present invention, the aluminumalloy composition is any one of aluminum alloy compositions (1) to (7)below.

Aluminum Alloy Composition (1)

0.30 mass% or less of Si, more than 0.35 mass% of Fe, 0.20 mass% or lessof Cu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% of Mg, 0.30 mass% orless of Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or less of V, 0.25 mass%or less of Zr, and 0.20 mass% or less of Ti, while additionallycontaining Al.

Aluminum Alloy Composition (2)

0.12 mass% or less of Si, more than 0.15 mass% of Fe, 1.5 to 2.0 mass%of Cu, 0.10 mass% or less of Mn, 2.1 to 2.6 mass% of Mg, 0.05 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.05 mass% or less of Ni, 0.10 to0.16 mass% of Zr, and 0.06 mass% or less of Ti, while additionallycontaining Al.

Aluminum Alloy Composition (3)

0.12 mass% or less of Si, more than 0.25 mass% of Fe, 2.0 to 2.6 mass%of Cu, 0.10 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.06mass% or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (4)

0.40 mass% or less of Si, more than 0.50 mass% of Fe, 1.2 to 2.0 mass%of Cu, 0.30 mass% or less of Mn, 2.1 to 2.9 mass% of Mg, 0.18 to 0.26mass% of Cr, 5.1 to 6.1 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

Aluminum Alloy Composition (5)

More than 0.7 mass% of Si+Fe, 0.10 mass% or less of Cu, 0.10 mass% orless of Mn, 0.10 mass% or less of Mg, and 0.8 to 1.3 mass% of Zn, whileadditionally containing Al.

Aluminum Alloy Composition (6)

0.12 mass% or less of Si, more than 0.12 mass% of Fe, 2.0 to 2.6 mass%of Cu, 0.06 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.05mass% or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (7)

0.40 mass% or less of Si, more than 0.50 mass% of Fe, 1.6 to 2.4 mass%of Cu, 0.30 mass% or less of Mn, 2.4 to 3.1 mass% of Mg, 0.18 to 0.28mass% of Cr, 6.3 to 7.3 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

By having such features, the aluminum alloy material of the presentinvention can effectively prevent or inhibit hydrogen embrittlement. Inparticular, it is possible to effectively prevent or inhibit hydrogenembrittlement to the extent required in the aerospace industry.

In the past, there have been a variety of discussions regarding therelationship between metal structures and hydrogen embrittlement. Asmeans for preventing hydrogen embrittlement, three types ofmicrostructure control methods have been proposed, namely (i) making thedistribution of precipitates at grain boundaries low density and coarse,(ii) making the grain boundary tilt angle (twist angle) small (astructure is not recrystallized), and (iii) refining crystal grains (forexample, see Goro ITOH, Takehiko ETOH, Yoshimitsu MIYAGI, MikihiroKANNO, “Al-Zn-Mg-based alloy”, Light Metals, 38 (1988), pages 818 to839. Moreover, in the table on page 822, a tetragonal Al₇Cu₂Fe crystalis described as a stable phase). However, the effectiveness of thesemeans is unclear, and specific mechanisms are also unclear. Although theeffectiveness thereof is insufficient, addition of alloying elementssuch as zirconium and chromium, which is actually carried out as amethod for preventing hydrogen embrittlement, was based on method (ii)or (iii) above.

In the present invention, however, attention was paid to the fact thatlocal distribution behavior and accumulation behavior of hydrogen in thealuminum alloy material govern hydrogen embrittlement cracks. Particularattention was paid to the fact that a controlling factor responsible forhydrogen embrittlement was hydrogen trapped in precipitates (seeEngineering Fracture Mechanics 216 (2019) 106503). In addition, theamount of hydrogen at hydrogen trapping sites that causes hydrogenembrittlement was grasped by determining the binding energy betweenaluminum microstructures and hydrogen and calculating the hydrogendistribution in the aluminum alloy material. An aluminum alloy materialhaving a specific alloy composition was found that can effectivelyprevent or inhibit hydrogen embrittlement in an aluminum alloy byconcentrating hydrogen at sites that can strongly trap hydrogen. Inaddition, it was found that second phase particles having a higherhydrogen trapping energy than that of a semi-coherent precipitateinterface are used as the hydrogen trapping site.

In addition, the hydrogen embrittlement inhibitor for aluminum alloymaterials of the present invention, which is described later, comprisesAl₇Cu₂Fe particles having the hydrogen trapping sites mentioned above.

Moreover, hydrogen embrittlement cracks include grain boundary cracksand quasi-cleavage cracks, and quasi-cleavage cracks in particular canbe effectively prevented or inhibited in the present invention.

Preferred aspects of the present invention will now be explained.

<Aluminum Alloy Composition>

In the aluminum alloy material of the present invention, the aluminumalloy composition is any one of aluminum alloy compositions (1) to (7)above.

Among these aluminum alloy compositions, the aluminum alloy compositionis preferably aluminum alloy composition (3) above in the presentinvention.

The aluminum alloy material of the present invention preferably has anFe content of more than 0.12 mass%, more preferably more than 0.15mass%, particularly preferably more than 0.25 mass%, and yet morepreferably 0.30 mass% or more, relative to the entire aluminum alloymaterial. As the amount of Fe increases, the volume ratio of the secondphase particles (preferably Al₇Cu₂Fe particles), the number density ofthe second phase particles, and the particle diameter of the secondphase particles can also be increased.

However, the upper limit of the amount of Fe is not particularlylimited. For example, the amount of Fe relative to the entire aluminumalloy material can be, for example, 1.0 mass% or less, 0.8 mass% orless, or 0.6 mass% or less. If the amount of Fe is less than these upperlimits, the volume ratio, number density and particle size of the secondphase particles are reduced to a certain extent, meaning that it iseasier to inhibit deterioration of material properties caused byaggregation and localization of second phase particles.

The aluminum alloy material of the present invention contains aluminumas a primary component, and preferably contains 0.50 mass% or more ofaluminum.

More preferred ranges for the aluminum alloy composition will bedescribed in order.

Aluminum alloy composition (1) is as shown below.

0.30 mass% or less of Si, more than 0.35 mass% of Fe, 0.20 mass% or lessof Cu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% of Mg, 0.30 mass% orless of Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or less of V, 0.25 mass%or less of Zr, and 0.20 mass% or less of Ti, while additionallycontaining Al.

In aluminum alloy composition (1), the content of Fe is preferably morethan 0.35 mass% and not more than 1.0 mass%, and more preferably morethan 0.35 mass% and not more than 0.6 mass%.

Aluminum alloy composition (2) is as shown below.

0.12 mass% or less of Si, more than 0.15 mass% of Fe, 1.5 to 2.0 mass%of Cu, 0.10 mass% or less of Mn, 2.1 to 2.6 mass% of Mg, 0.05 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.05 mass% or less of Ni, 0.10 to0.16 mass% of Zr, and 0.06 mass% or less of Ti, while additionallycontaining Al.

In aluminum alloy composition (2), the content of Fe is preferably morethan 0.15 mass% and not more than 1.0 mass%, and more preferably morethan 0.15 mass% and not more than 0.6 mass%.

Aluminum alloy composition (3) is as shown below.

0.12 mass% or less of Si, more than 0.25 mass% of Fe, 2.0 to 2.6 mass%of Cu, 0.10 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.06mass% or less of Ti, while additionally containing Al.

In aluminum alloy composition (3), the content of Fe is preferably morethan 0.25 mass% and not more than 1.0 mass%, and more preferably morethan 0.25 mass% and not more than 0.6 mass%.

Aluminum alloy composition (4) is as shown below.

0.40 mass% or less of Si, more than 0.50 mass% of Fe, 1.2 to 2.0 mass%of Cu, 0.30 mass% or less of Mn, 2.1 to 2.9 mass% of Mg, 0.18 to 0.26mass% of Cr, 5.1 to 6.1 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

In aluminum alloy composition (4), the content of Fe is preferably morethan 0.55 mass% and not more than 1.0 mass%, and more preferably morethan 0.55 mass% and not more than 0.6 mass%.

Aluminum alloy composition (5) is as shown below.

More than 0.7 mass% of Si+Fe, 0.10 mass% or less of Cu, 0.10 mass% orless of Mn, 0.10 mass% or less of Mg, and 0.8 to 1.3 mass% of Zn, whileadditionally containing Al.

In aluminum alloy composition (5), it is preferable for 0.7 mass%<Si+Fe≤ 1.0 mass%. In addition, the content of Fe is preferably more than 0.35mass% and not more than 1.0 mass%, and more preferably more than 0.35mass% and not more than 0.6 mass%.

Aluminum alloy composition (6) is as shown below.

0.12 mass% or less of Si, more than 0.12 mass% of Fe, 2.0 to 2.6 mass%of Cu, 0.06 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.05mass% or less of Ti, while additionally containing Al.

In aluminum alloy composition (6), the content of Fe is preferably morethan 0.12 mass% and not more than 1.0 mass%, and more preferably morethan 0.12 mass% and not more than 0.6 mass%.

Aluminum alloy composition (7) is as shown below.

0.40 mass% or less of Si, more than 0.50 mass% of Fe, 1.6 to 2.4 mass%of Cu, 0.30 mass% or less of Mn, 2.4 to 3.1 mass% of Mg, 0.18 to 0.28mass% of Cr, 6.3 to 7.3 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

In aluminum alloy composition (7), the content of Fe is preferably morethan 0.50 mass% and not more than 1.0 mass%, and more preferably morethan 0.50 mass% and not more than 0.6 mass%.

<Shape of Alloy Material>

The shape of the aluminum alloy material of the present invention is notparticularly limited. The aluminum alloy material may be bulky orparticulate, but is preferably bulky.

<Second Phase Particles>

The aluminum alloy material of the present invention preferably containssecond phase particles having a higher hydrogen trapping energy thanthat of a semi-coherent precipitate interface.

The term second phase particles means particles having a compositionthat is different from the constituent composition of a parent phase.The second phase particles in the aluminum alloy material are particleshaving a composition that is different from that of Al or the aluminumalloy material.

Second phase particles having a higher hydrogen trapping energy thanthat of a semi-coherent precipitate interface are not particularlylimited. Second phase particles having a higher hydrogen trapping energythan that of a semi-coherent precipitate interface can be determinedusing first principle calculations. The term “first principlecalculations” means theoretically representing an electronic state bymathematically solving the Schrodinger equation (without usingexperimental data or empirical parameters). The distribution of hydrogenat each trapping site can be calculated from the density of otherhydrogen trapping sites, such as grain boundaries, precipitates andlattices, and the binding energy with hydrogen. Moreover, by observingthe deformation process of the aluminum alloy material by radiationtomography and carrying out 3D or 4D image processing, a large number ofsecond phase particles dispersed in the aluminum alloy material can betraced, and the internal plastic strain distribution can be determinedby means of 3D mapping. From the 3D strain distribution, geometricallyrequired dislocations, statistically required dislocations, andconcentration distributions of atomic vacancies can be calculated.

In the present invention, second phase particles having a hydrogentrapping energy higher than that of a semi-coherent precipitateinterface are preferably Al₇Cu₂Fe particles. Moreover, similar effectscan be expected from particles having an Al:Cu:Fe atomic ratio thatdeviates from the stoichiometric composition of 7:2:1 by approximately30% (for example, Al₇Cu₂Fe_(0.7) particles). Of the hydrogen trappingenergies of the microstructures in the aluminum alloy material, that ofAl₇Cu₂Fe particles is 0.56 eV. However, preferred second phase particlesor microstructures other than Al₇Cu₂Fe particles having hydrogentrapping energies that are higher than that of a semi-coherentprecipitate interface (0.55 eV) are not yet known.

The shape of the second phase particles includes a variety of shapes,such as spherical, elliptical, square cylinder-shaped, cylindrical,cubic, rectangular parallelepiped-shaped and scaly, but is preferablyspherical or elliptical.

The volume ratio of the second phase particles is preferably 0.05 to10.0%, more preferably 0.1 to 5.0%, and particularly preferably 0.5 to2.0%. The volume ratio of the second phase particles can be calculatedas the volume of the second phase particles relative to the volume ofthe aluminum alloy material by means of, for example, 3D analysis usingX-Ray tomography (CT).

The number density of the second phase particles is preferably6.5×10¹²/m³ to 100×10¹²/m³, more preferably 10×10¹²/m³ to 50×10¹²/m³,and particularly preferably 20×10¹²/m³ to 40×10¹²/m³. The number densityof the second phase particles can be calculated by means of, forexample, 3D analysis using high resolution X-Ray tomography (CT) havinga spatial resolution of up to 1 µm.

The average particle diameter of the second phase particles ispreferably 0.5 to 20 µm. The upper limit of the average particlediameter of the second phase particles is preferably 10 µm or less, andparticularly preferably 5.0 µm or less. The average particle diameter ofthe second phase particles can be calculated as an arithmetic mean valueby means of, for example, 3D analysis using X-Ray tomography (CT).

<Method for Producing Aluminum Alloy Material>

The method for producing the aluminum alloy material is notparticularity limited.

By forming the hydrogen embrittlement inhibitor for aluminum alloymaterials, which comprises Al₇Cu₂Fe particles, inside a raw materialaluminum alloy material, it is possible to prevent hydrogenembrittlement in the aluminum alloy material.

It is possible to add Al₇Cu₂Fe particles to the raw material aluminumalloy material, or to add Fe at the time of production to form Al₇Cu₂Feparticles, and ultimately use the Al₇Cu₂Fe particles as a hydrogenembrittlement inhibitor.

The raw material aluminum alloy material may be a raw material mixturebefore a metal such as Al or a metal compound is alloyed.

The aluminum alloy material can be produced by subjecting the rawmaterial aluminum alloy material (which may be a raw material mixture)to a well-known process such as a heat treatment, rolling, forgingand/or casting. In the present invention, it is preferable to cast theraw material aluminum alloy material to produce the aluminum alloymaterial from the perspective of inhibiting hydrogen trapping inprecipitates, that is, inhibiting quasi-cleavage creak. In particular,it is preferable to actively form Al₇Cu₂Fe particles by adding Fe at thetime of casting to the raw material mixture before each metal or metalcompound is alloyed, at a higher quantity than in a case where aconventional aluminum alloy material is produced. In addition, it ispossible to not carry out a heat treatment, rolling or forging.

As other production methods, the method described in paragraphs [0034]to [0042] of Japanese Patent Application Publication No. 2009-221556 canbe appropriated, and the contents of this publication are incorporatedherein by reference.

Hydrogen Embrittlement Inhibitor for Aluminum Alloy Materials

The hydrogen embrittlement inhibitor for aluminum alloy materials of thepresent invention comprises Al₇Cu₂Fe particles and can prevent hydrogenembrittlement of aluminum alloy materials.

Al₇Cu₂Fe particles may be contained in an existing aluminum alloymaterial, but such a product was not known to be a hydrogenembrittlement inhibitor for aluminum alloy materials.

<Raw Material Aluminum Alloy Material>

The raw material aluminum alloy material in which hydrogen embrittlementis to be prevented may be the aluminum alloy material of the presentinvention or a conventional aluminum alloy material.

It is preferable for the hydrogen embrittlement inhibitor for aluminumalloy materials of the present invention to be able to prevent hydrogenembrittlement of an aluminum alloy material having aluminum alloycomposition (A) below.

Aluminum Alloy Composition (A)

0.40 mass% or less of Si, 2.6 mass% or less of Cu, 0.70 mass% or less ofMn, 3.1 mass% or less of Mg, 0.30 mass% or less of Cr, 7.3 mass% or lessof Zn, and 0.20 mass% or less of Ti, while additionally containing Feand Al.

In a case where a raw material aluminum alloy material in which hydrogenembrittlement is to be prevented is the aluminum alloy material of thepresent invention, it is preferable for the hydrogen embrittlementinhibitor for aluminum alloy materials of the present invention to beable to prevent hydrogen embrittlement in an aluminum alloy materialhaving any one of aluminum alloy compositions (1) to (7) above.

In a case where a raw material aluminum alloy material in which hydrogenembrittlement is to be prevented is a conventional aluminum alloymaterial, it is preferable for the hydrogen embrittlement inhibitor foraluminum alloy materials of the present invention to be able to preventhydrogen embrittlement in an aluminum alloy material having any one ofaluminum alloy compositions (A1) to (A7) below. However, in a case wherea raw material aluminum alloy material in which hydrogen embrittlementis to be prevented is a conventional aluminum alloy material, it ispreferable to reduce the particle diameter of second phase particles tolower than in the past and disperse these second phase particles so asto more readily prevent hydrogen embrittlement.

Aluminum Alloy Composition (A1)

0.30 mass% or less of Si, 0.35 mass% or less of Fe, 0.20 mass% or lessof Cu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% of Mg, 0.30 mass% orless of Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or less of V, 0.25 mass%or less of Zr, and 0.20 mass% or less of Ti, while additionallycontaining Al.

Aluminum Alloy Composition (A2)

0.12 mass% or less of Si, 0.15 mass% or less of Fe, 1.5 to 2.0 mass% ofCu, 0.10 mass% or less of Mn, 2.1 to 2.6 mass% of Mg, 0.05 mass% or lessof Cr, 5.7 to 6.7 mass% of Zn, 0.05 mass% or less of Ni, 0.10 to 0.16mass% of Zr, and 0.06 mass% or less of Ti, while additionally containingAl.

Aluminum Alloy Composition (A3)

0.12 mass% or less of Si, 0.15 mass% or less of Fe, 2.0 to 2.6 mass% ofCu, 0.10 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% or lessof Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.06 mass%or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (A4)

0.40 mass% or less of Si, 0.50 mass% or less of Fe, 1.2 to 2.0 mass% ofCu, 0.30 mass% or less of Mn, 2.1 to 2.9 mass% of Mg, 0.18 to 0.26 mass%of Cr, 5.1 to 6.1 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al. Aluminum alloy composition (A5)

0.7 mass% or less of Si+Fe, 0.10 mass% or less of Cu, 0.10 mass% or lessof Mn, 0.10 mass% or less of Mg, and 0.8 to 1.3 mass% of Zn, whileadditionally containing Al.

Aluminum Alloy Composition (A6)

0.12 mass% or less of Si, 0.12 mass% or less of Fe, 2.0 to 2.6 mass% ofCu, 0.06 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% or lessof Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.05 mass%or less of Ti, while additionally containing Al.

Aluminum Alloy Composition (A7)

0.40 mass% or less of Si, 0.50 mass% or less of Fe, 1.6 to 2.4 mass% ofCu, 0.30 mass% or less of Mn, 2.4 to 3.1 mass% of Mg, 0.18 to 0.28 mass%of Cr, 6.3 to 7.3 mass% of Zn, and 0.20 mass% or less of Ti, whileadditionally containing Al.

Aluminum alloy compositions (A1) to (A7) are summarized in Table 1below. “Alloy number” in Table 1 means the alloy number in JIS H 4100:2014 “Aluminum and aluminum alloy plates and strips”.

TABLE 1 Alloy Composition Alloy No. Laminated sheet Si Fe Cu Mn Mg Cr ZnGa, V, Ni, B, Zr etc. Ti Others Al Each Total (A1 ) 7204 (7N01 ) ≤0.30≤0.35 ≤0.20 0.20-0.7 1.0-2.0 ≤0.30 4.0-5.0 V: ≤0.10, Zr: ≤0.25 ≤0.20≤0.05 ≤0.15 Balance (A2) 7010 ≤0.12 ≤0.15 1.5-2.0 ≤0.10 2.1-2.6 ≤0.055.7-6.7 Ni: ≤0.05, Zr: 0.10-0.16 ≤0.06 ≤0.05 ≤0.15 Balance (A3) 7050≤0.12 ≤0.15 2.0-2.6 ≤0.10 1.9-2.6 ≤0.04 5.7-6.7 Zr: 0.08-0.15 ≤0.06≤0.05 ≤0.15 Balance (A4) 7075 ≤0.40 ≤0.50 1.2-2.0 ≤0.30 2.1-2.90.18-0.28 5.1-6.1 - ≤0.20 ≤0.05 ≤0.15 Balance 7075 Laminated sheet Corematerial (7075) ≤0.40 ≤0.50 1.2-2.0 ≤0.30 2.1-2.9 0.18-0.28 5.1-6.1 -≤0.20 ≤0.05 ≤0.15 Balance (A5) Skin material (7072) Si+Fe: ≤0.7 ≤0.10≤0.10 ≤0.10 - 0.8-1.3 - - ≤0.05 ≤0.15 Balance (A6) 7475 ≤0.10 ≤0.121.2-1.9 ≤0.06 1.9-2.6 0.18-0.25 5.2-6.2 - ≤0.06 ≤0.05 ≤0.15 Balance (A7)7178 ≤0.40 ≤0.50 1.6-2.4 ≤0.30 2.4-3.1 0.18-0.28 6.3-7.3 - ≤0.20 ≤0.05≤0.15 Balance

WORKING EXAMPLES

The present invention will now be explained in greater detail by meansof working examples and comparative examples. The materials, usagequantities, ratios, treatment details, treatment procedures, and so on,shown in the working examples below can be changed as appropriate aslong as these do not deviate from the gist of the present invention.Therefore, the scope of the present invention should not be interpretedas being limited by the specific examples given below.

Working Example 1

Using the method described below, an aluminum alloy material (High Fe)of Working Example 1, in which content of Fe was 0.30 mass%, wasprepared as an aluminum alloy material that satisfies aluminum alloycomposition (3). This aluminum alloy material is an Al-Zn-Cu alloy whichcontains 50 mass% or more of Al as a primary component, with thecomponent having the next highest content being Zn, followed by Cu.

Fe was further added to a melting column for the composition of AlloyNo. 7050 in JIS H 4100: 2014 “Aluminum and Aluminum Alloy Plates andStrips”, that is, a material for casting an aluminum alloy material thatsatisfies the aluminum alloy composition (A3), and Al₇Cu₂Fe particleswere formed inside the material as second phase particles.

Reference Examples 1 and 2

An aluminum alloy (Mid Fe) of Reference Example 1, in which the contentof Fe was 0.05 mass%, and an aluminum alloy material (Low Fe) ofReference Example 2, in which the content of Fe was 0.01 mass%, wereprepared as aluminum alloy materials that satisfy the composition ofAlloy No. 7050 in JIS H 4100: 2014 “Aluminum and Aluminum Alloy Platesand Strips”, that is, aluminum alloy composition (A3).

[Evaluations] <3D Analysis>

The aluminum alloy materials of Working Example 1 and Reference Examples1 and 2 were subjected to 3D analysis by means of X-Ray tomography. Theobtained results are shown in Table 2 below. In Table 2 below,“Particles” means Al₇Cu₂Fe particles.

TABLE 2 Material Amount of Fe (mass%) Volume ratio of particles (%)Number density of particles (10¹²/m³) Particle diameter (µm) High Fe0.30 1.0 35.2 4.6 Mid Fe 0.05 0.1 6.7 1.7 Low Fe 0.01 0.05 6.3 1.7

From Table 2 above, it was understood that the volume ratio of Al₇Cu₂Feparticles also increased as the amount of Fe increased.

<Tomographic Images>

Next, tomographic images were taken of the aluminum alloy materials ofWorking Example 1 and Reference Examples 1 and 2.

FIG. 1 shows a virtual cross section of a tomographic image of amicrostructure of the (High Fe) aluminum alloy material of WorkingExample 1. In addition, FIG. 2 shows a virtual cross section of atomographic image of a fracture surface of the (High Fe) aluminum alloymaterial of Working Example 1. In FIG. 2 and FIG. 4 , QCF means Areafraction of Quasi-cleavage creak.

FIG. 3 shows a virtual cross section of a tomographic image of the (LowFe) aluminum alloy material of Reference Example 2. In addition, FIG. 4shows a virtual cross section of a tomographic image of a fracturesurface of the (Low Fe) aluminum alloy material of Reference Example 2.

Diagrams are not shown for Reference Example 1.

From FIG. 1 , it was understood that in the (High Fe) aluminum alloymaterial of Working Example 1, second phase particles, namely Al₇Cu₂Feparticles, were formed inside the material. It was also understood thatthe Al₇Cu₂Fe particles were present at the micron level, and weredispersed at a high density.

However, in the (Low Fe) aluminum alloy material of Reference Example 2shown in FIG. 3 , it was understood that the second phase particles werehardly formed inside the material.

Furthermore, from FIG. 2 and FIG. 4 and the results of Reference Example1 (not shown), the area fraction of quasi-cleavage creak (QCF) atfracture surfaces was determined for Working Example 1 (High Fe),Reference Example 1 (Mid Fe) and Reference Example 2 (Low Fe). Theobtained results are shown in Table 3 below.

TABLE 3 Area fraction of quasi-cleavage creak QCF (%) High Fe (0.30mass%) 8.1 Mid Fe (0.05 mass%) 18.8 Low Fe (0.01 mass%) 22.4

In view of Table 3 above, hydrogen embrittlement can be reduced. It wasunderstood that when the amount of Fe increases from 0.01 mass% to 0.3mass%, the area fraction of quasi-cleavage creak (QCF) decreases from22.4% to 8.1%. The area fraction of quasi-cleavage creak QCF correspondsto the hydrogen embrittlement fracture surface ratio. It was thusunderstood that hydrogen embrittlement can be reduced by increasing theamount of Fe in comparison with conventional aluminum alloy materials,to form and disperse at the micron level at a high density Al₇Cu₂Feparticles as second phase particles inside the material. In addition, itwas found that Al₇Cu₂Fe particles can effectively prevent or inhibitquasi-cleavage creak of the aluminum alloy material, and are extremelyeffective as a hydrogen embrittlement inhibitor for aluminum alloymaterials.

<Analysis of Hydrogen Distribution State>

For the aluminum alloy materials of Working Example 1, Reference Example1 and Reference Example 2, the hydrogen amount (H at IMC) in amicrostructure and the hydrogen amount (H at η₂) in a semi-coherentprecipitate (η₂, semi-coherent) were determined using a calculationprocess.

Semi-Spontaneous Separation of Semi-coherent Precipitate Interface ByHydrogen

Separation of a η/Al interface by hydrogen trapping was calculated usingfirst principle calculations. The obtained results are shown in FIG. 5 .

From FIG. 5 , it was understood that when hydrogen was concentrated at asemi-coherent precipitate interface (η₂, semi-coherent), the interfacesemi-spontaneously separated, and this separation became a startingpoint for hydrogen embrittlement. This result is a new hydrogenembrittlement mechanism in aluminum alloy materials.

Hydrogen Trapping Energies of Microstructures

The hydrogen trapping energies of microstructures in the aluminum alloymaterial were calculated using first principle calculations. Theobtained results are shown in FIG. 6 . In FIG. 6 , spiral dislocations(Screw disl.), solute Mg atoms (Solute Mg), edge dislocations (Edgedisl.), grain boundaries (GB), vacancies (Vac.), coherent precipitateinterfaces (η₁, coherent), semi-coherent precipitate interfaces (η₂,semi-coherent), Al₇Cu₂Fe particles (IMCp), pore surface (Pore (surfaceH), and molecular hydrogen in the pore (Pore (H₂)) are shown in orderfrom the left.

From FIG. 6 , it was understood that in the control of hydrogenembrittlement, microstructure control by heat treatment or rolling isnot effective for inhibiting hydrogen trapping in precipitates, that is,is not effective for suppressing quasi-cleavage creak. It was understoodthat the binding energy between a precipitate and hydrogen was thesecond highest after a pore, and the trapping site density of hydrogenwas also high. It was understood that in order to inhibit quasi-cleavagecreak based on hydrogen distribution control, it is necessary to providea site in the material which has a higher binding energy with hydrogenthan a precipitate and a sufficiently high trapping site density. FromFIG. 6 , it was understood that among the hydrogen trapping energies ofthe microstructures, that of Al₇Cu₂Fe particles was 0.56 eV, which washigher than 0.35 eV for a coherent precipitate interface (η₁, coherent)and 0.55 eV for a semi-coherent precipitate interface (η₂,semi-coherent). That is, the Al₇Cu₂Fe particles have a higher hydrogentrapping energy than that of a semi-coherent precipitate interface, andthis is effective for preventing hydrogen embrittlement.

The crystal structure (space group P4/mnc) of the Al₇Cu₂Fe particles isshown in FIG. 7 (see Bown et al., Acta Cryst., 9 (1956), 911). From FIG.7 , it can be confirmed that there is a hydrogen trapping site that canstrongly trap H inside the Al₇Cu₂Fe particles.

Calculation of Hydrogen Distribution State

The hydrogen distribution state in the aluminum alloy material wasanalyzed.

Based on the relationships of Numerical Formulae 1 to 3 below, thedistribution state of hydrogen in a state of thermal equilibrium wascalculated using hydrogen trapping energies determined using firstprinciple calculations. Specific calculations were carried out using amethod according to Engineering Fracture Mechanics 216 (2019) 106503.

[Math. 1]

Formula 1: Thermal equilibrium

[Math. 2]

Formula 2: Distribution of hydrogen at trapping sites

[Math. 3]

Formula 3: Reduction in surface E (surface energy) of pore due tohydrogen adsorption

The obtained results are shown in FIG. 8 . In FIG. 8 , amounts ofhydrogen trapped in microstructures of lattices (Lattice), solute Mgatoms (Mg), pores (V), grain boundaries (_(┴)), Al₇Cu₂Fe particles(IMCp), coherent precipitate interfaces (coherent), semi-coherentprecipitate interfaces (semi-coherent) and pores (Pore), respectively,are shown in order from the left. In the two bar charts for eachmicrostructure, the left hand bar shows a case where the amount of Fe is0.30 mass% (High Fe), which corresponds to Working Example 1, and theright hand bar shows a case where the amount of Fe is 0.01 mass% (LowFe), which corresponds to Reference Example 2. However, results for acase where the amount of Fe is 0.05 mass% (Mid Fe), which corresponds toReference Example 1, are not shown in FIG. 8 .

As shown in FIG. 8 , it can be understood that hydrogen in the aluminumalloy material is distributed at each microstructure according to thetrapping energy thereof.

In an aluminum alloy material having a low Fe amount of 0.01 mass% (LowFe), which is similar to that of Reference Example 1, hydrogen is moststrongly distributed at a semi-coherent precipitate interface (η₂,semi-coherent). This is a starting point for hydrogen embrittlement (seeFIG. 5 above).

On the other hand, in an aluminum alloy having a high Fe amount of 0.30mass% (High Fe), which is similar to Working Example 1, hydrogen is moststrongly distributed at Al₇Cu₂Fe particles (IMCp). As a result, it wasunderstood that the hydrogen concentration at a precipitate interfacesuch as a semi-coherent precipitate (η₂, semi-coherent) interface wasreduced, and hydrogen embrittlement could be prevented.

The evaluation results above are summarized in FIG. 9 . FIG. 9 is agraph that shows the relationship between hydrogen distribution to IMC(Al₇Cu₂Fe) particles (H at IMC), hydrogen distribution to asemi-coherent precipitate interface (H at η₂), and hydrogenembrittlement (quasi-cleavage creak) area fraction QCF. The horizontalaxis shows the amount of Fe in the aluminum alloy materials of WorkingExample 1, Reference Example 1 and Reference Example 2.

From Table 1 above, it was understood that the volume ratio of theAl₇Cu₂Fe particles increases as the amount of Fe in the aluminum alloymaterial increases.

From the results in Table 1 and FIG. 9 , it was understood that as theamount of Fe in the aluminum alloy material increases, the amount ofhydrogen trapped by Al₇Cu₂Fe particles increases (dashed line; H atIMC), the amount of hydrogen in the precipitate decreases (H at η₂), andhydrogen embrittlement (quasi-cleavage creak) can be effectivelyprevented or inhibited (QCF).

In addition, it was understood that the aluminum alloy materialeffectively functions as a hydrogen brittle inhibitor even in a casewhere a material for casting an aluminum alloy material having aconventional well-known composition specified in JIS H 4100: 2014 isused, because Al₇Cu₂Fe particles are formed inside the material assecond phase particles.

1. An aluminum alloy material which has an aluminum alloy composition ofany one of aluminum alloy compositions (1) to (7) below. Aluminum alloycomposition (1) 0.30 mass% or less of Si, more than 0.35 mass% of Fe,0.20 mass% or less of Cu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% ofMg, 0.30 mass% or less of Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or lessof V, 0.25 mass% or less of Zr, and 0.20 mass% or less of Ti, whileadditionally containing Al. Aluminum alloy composition (2) 0.12 mass% orless of Si, more than 0.15 mass% of Fe, 1.5 to 2.0 mass% of Cu, 0.10mass% or less of Mn, 2.1 to 2.6 mass% of Mg, 0.05 mass% or less of Cr,5.7 to 6.7 mass% of Zn, 0.05 mass% or less of Ni, 0.10 to 0.16 mass% ofZr, and 0.06 mass% or less of Ti, while additionally containing Al.Aluminum alloy composition (3) 0.12 mass% or less of Si, more than 0.25mass% of Fe, 2.0 to 2.6 mass% of Cu, 0.10 mass% or less of Mn, 1.9 to2.6 mass% of Mg, 0.04 mass% or less of Cr, 5.7 to 6.7 mass% of Zn, 0.08to 0.15 mass% of Zr, and 0.06 mass% or less of Ti, while additionallycontaining Al. Aluminum alloy composition (4) 0.40 mass% or less of Si,more than 0.50 mass% of Fe, 1.2 to 2.0 mass% of Cu, 0.30 mass% or lessof Mn, 2.1 to 2.9 mass% of Mg, 0.18 to 0.26 mass% of Cr, 5.1 to 6.1mass% of Zn, and 0.20 mass% or less of Ti, while additionally containingAl. Aluminum alloy composition (5) More than 0.7 mass% of Si+Fe, 0.10mass% or less of Cu, 0.10 mass% or less of Mn, 0.10 mass% or less of Mg,and 0.8 to 1.3 mass% of Zn, while additionally containing Al. Aluminumalloy composition (6) 0.12 mass% or less of Si, more than 0.12 mass% ofFe, 2.0 to 2.6 mass% of Cu, 0.06 mass% or less of Mn, 1.9 to 2.6 mass%of Mg, 0.04 mass% or less of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15mass% of Zr, and 0.05 mass% or less of Ti, while additionally containingAl. Aluminum alloy composition (7) 0.40 mass% or less of Si, more than0.50 mass% of Fe, 1.6 to 2.4 mass% of Cu, 0.30 mass% or less of Mn, 2.4to 3.1 mass% of Mg, 0.18 to 0.28 mass% of Cr, 6.3 to 7.3 mass% of Zn,and 0.20 mass% or less of Ti, while additionally containing Al.
 2. Thealuminum alloy material set forth in claim 1 in which the aluminum alloycomposition is aluminum alloy composition (3).
 3. The aluminum alloymaterial set forth in claim 1, which includes second phase particleshaving a higher hydrogen trapping energy than that of a semi-coherentprecipitate interface.
 4. The aluminum alloy material set forth in claim3, wherein the second phase particles are Al₇Cu₂Fe particles.
 5. Ahydrogen embrittlement inhibitor for aluminum alloy materials, whichcomprises Al₇Cu₂Fe particles and can prevent hydrogen embrittlement ofaluminum alloy materials.
 6. The hydrogen embrittlement inhibitor setforth in claim 5, which can prevent hydrogen embrittlement of analuminum alloy material having aluminum alloy composition (A) below.Aluminum alloy composition (A) 0.40 mass% or less of Si, 2.6 mass% orless of Cu, 0.70 mass% or less of Mn, 3.1 mass% or less of Mg, 0.30mass% or less of Cr, 7.3 mass% or less of Zn, and 0.20 mass% or less ofTi, while additionally containing Fe and Al.
 7. The hydrogenembrittlement inhibitor set forth in claim 5, which can prevent hydrogenembrittlement of an aluminum alloy material having any one of aluminumalloy compositions (1) to (7) below. Aluminum alloy composition (1) 0.30mass% or less of Si, more than 0.35 mass% of Fe, 0.20 mass% or less ofCu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% of Mg, 0.30 mass% or lessof Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or less of V, 0.25 mass% orless of Zr, and 0.20 mass% or less of Ti, while additionally containingAl. Aluminum alloy composition (2) 0.12 mass% or less of Si, more than0.15 mass% of Fe, 1.5 to 2.0 mass% of Cu, 0.10 mass% or less of Mn, 2.1to 2.6 mass% of Mg, 0.05 mass% or less of Cr, 5.7 to 6.7 mass% of Zn,0.05 mass% or less of Ni, 0.10 to 0.16 mass% of Zr, and 0.06 mass% orless of Ti, while additionally containing Al. Aluminum alloy composition(3) 0.12 mass% or less of Si, more than 0.25 mass% of Fe, 2.0 to 2.6mass% of Cu, 0.10 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04mass% or less of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr,and 0.06 mass% or less of Ti, while additionally containing Al. Aluminumalloy composition (4) 0.40 mass% or less of Si, more than 0.50 mass% ofFe, 1.2 to 2.0 mass% of Cu, 0.30 mass% or less of Mn, 2.1 to 2.9 mass%of Mg, 0.18 to 0.26 mass% of Cr, 5.1 to 6.1 mass% of Zn, and 0.20 mass%or less of Ti, while additionally containing Al. Aluminum alloycomposition (5) More than 0.7 mass% of Si+Fe, 0.10 mass% or less of Cu,0.10 mass% or less of Mn, 0.10 mass% or less of Mg, and 0.8 to 1.3 mass%of Zn, while additionally containing Al. Aluminum alloy composition (6)0.12 mass% or less of Si, more than 0.12 mass% of Fe, 2.0 to 2.6 mass%of Cu, 0.06 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% orless of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.05mass% or less of Ti, while additionally containing Al. Aluminum alloycomposition (7) 0.40 mass% or less of Si, more than 0.50 mass% of Fe,1.6 to 2.4 mass% of Cu, 0.30 mass% or less of Mn, 2.4 to 3.1 mass% ofMg, 0.18 to 0.28 mass% of Cr, 6.3 to 7.3 mass% of Zn, and 0.20 mass% orless of Ti, while additionally containing Al.
 8. The hydrogenembrittlement inhibitor set forth in claim 5, which can prevent hydrogenembrittlement of an aluminum alloy material having any one of aluminumalloy compositions (A1) to (A7) below. Aluminum alloy composition (A1)0.30 mass% or less of Si, 0.35 mass% or less of Fe, 0.20 mass% or lessof Cu, 0.20 to 0.70 mass% of Mn, 1.0 to 2.0 mass% of Mg, 0.30 mass% orless of Cr, 4.0 to 5.0 mass% of Zn, 0.10 mass% or less of V, 0.25 mass%or less of Zr, and 0.20 mass% or less of Ti, while additionallycontaining Al. Aluminum alloy composition (A2) 0.12 mass% or less of Si,0.15 mass% or less of Fe, 1.5 to 2.0 mass% of Cu, 0.10 mass% or less ofMn, 2.1 to 2.6 mass% of Mg, 0.05 mass% or less of Cr, 5.7 to 6.7 mass%of Zn, 0.05 mass% or less of Ni, 0.10 to 0.16 mass% of Zr, and 0.06mass% or less of Ti, while additionally containing Al. Aluminum alloycomposition (A3) 0.12 mass% or less of Si, 0.15 mass% or less of Fe, 2.0to 2.6 mass% of Cu, 0.10 mass% or less of Mn, 1.9 to 2.6 mass% of Mg,0.04 mass% or less of Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% ofZr, and 0.06 mass% or less of Ti, while additionally containing Al.Aluminum alloy composition (A4) 0.40 mass% or less of Si, 0.50 mass% orless of Fe, 1.2 to 2.0 mass% of Cu, 0.30 mass% or less of Mn, 2.1 to 2.9mass% of Mg, 0.18 to 0.26 mass% of Cr, 5.1 to 6.1 mass% of Zn, and 0.20mass% or less of Ti, while additionally containing Al. Aluminum alloycomposition (A5) 0.7 mass% or less of Si+Fe, 0.10 mass% or less of Cu,0.10 mass% or less of Mn, 0.10 mass% or less of Mg, and 0.8 to 1.3 mass%of Zn, while additionally containing Al. Aluminum alloy composition (A6)0.12 mass% or less of Si, 0.12 mass% or less of Fe, 2.0 to 2.6 mass% ofCu, 0.06 mass% or less of Mn, 1.9 to 2.6 mass% of Mg, 0.04 mass% or lessof Cr, 5.7 to 6.7 mass% of Zn, 0.08 to 0.15 mass% of Zr, and 0.05 mass%or less of Ti, while additionally containing Al. Aluminum alloycomposition (A7) 0.40 mass% or less of Si, 0.50 mass% or less of Fe, 1.6to 2.4 mass% of Cu, 0.30 mass% or less of Mn, 2.4 to 3.1 mass% of Mg,0.18 to 0.28 mass% of Cr, 6.3 to 7.3 mass% of Zn, and 0.20 mass% or lessof Ti, while additionally containing Al.